Color display direct-view half-tone storage tube



March 15, 1966 L s YAGGY ETAL COLOR DISPLAY DIRECT-VIEW HALF-TONE STORAGE TUBE 2 Sheets-Sheet 1 Filed Sept. 4, 1962 2 Sheets-Sheet 2 Arrcoza! March 15, 1966 1.. s. YAGGY ETAL COLOR DISPLAY DIRECT-VIEW HALF-TONE STORAGE TUBE Filed Sept. 4., 1962 United States Patent 3,240,974 COLOR DISPLAY DIRECT-VIEW HALF-TONE STORAGE TUBE Leon S. Yaggy, North Carlsbad, and Chester D. Beintema,

Vista, Califi, assignors to Hughes Aircraft Company,

Culver City, Calif., a corporation of Delaware Filed ept. 4, 1962, Ser. No. 221,254 3 Claims. (Cl. 313-92) This invention relates to a direct-view half-tone type color storage tube. More particularly, the invention relates to a novel phosphor target or screen adapted to present a display wherein signals of diiferent intensities appear in different colors,

Color storage tubes are of particular interest in systems where it is desired to provide a visual display which discriminates between signals representing different kinds of information. Thus in certain types of radar systems it is often desirable to visually distinguish displays of targets moving at diiferent speeds, for example. In other radar systems such as for navigation, it is desirable to visually distinguish moving vehicles or aircraft, for example, from the background or terrain.

In U.S. Patent 2,962,623 issued to C. D. Beintema and assigned to the instant assignee, a color storage tube for these purposes is disclosed wherein a phosphor screen is utilized which comprises a plurality of phosphor elements which are in the form of dots surrounded by rings of phosphor material, the phosphor materials comprising the dots and rings being different whereby the dots emit light of one primary color and the rings light of a different primary color. By expanding or contracting the diameter of an electron beam coming through a storage grid aperture aligned with the dot, luminescence from the dot or from the dot and the ring can be obtained, thus providing a range of color from the primary color of the dot to mixtures of this primary color with the primary color of the ring.

The ring-dot phosphor arrangement while satisfactory for some purposes gives rise to some limitations which are avoided by the present invention. In the first place the usual arrangement is to utilize the less-efficient light emitting phosphor for the dot and a more eflicient light emitting phosphor for the ring, since the more efiicient phosphor would completely overpower the less eflicient phosphor unless the area of the more efiicient phosphor is restricted with respect to that of the less eflicient phosphor. Even though restriction of the area of the more efiicient phosphor ring was practiced, it was still very difiicult to control the transition from one color to another since only a small change in control voltage would cause the electron beam to expand onto the ring surrounding the dot on all sides simultaneously. In addition to precision control difficulties, this also meant that a large part of the available control range was not utilized.

Also, it is generally true that storage grids can be fabricated with superior quality and uniformity of aperture size using techniques which provide a square array of square holes rather than a triangular array of round holes. Since the phosphor pattern can best be registered or aligned with the storage grid by producing the former by means of the latter, using photographic techniques, a phosphor pattern is needed which can readily be generated photographically by means of a square array of square holes, if the superior quality and uniformity of such storage grids is to be utilized.

It will also be appreciated that the ring-dot configuration imposes a limitation on the number of color-producing elemental areas (rings and dots) which can be provided in a square array, thus limiting the resolution of the display. This is particularly true, Where, as in the aforementioned patent, each (lot is provided with its own particular ring.

It is therefore an object of the present invention to provide an improved half-tone color storage display tube.

Another object of the invention is to provide an improved half-tone color storage display tube having uniformity of color and brightness and better controllability of the transition from one color to another.

Still another object of the invention is to provide an improved half-tone color storage display tube of enhanced resolution.

These and other objects and advantages of the invention are achieved by providing a viewing screen having a plurality of phosphor areas capable of emitting light of one color, each such area having a plurality of phosphor areas capable of emitting light of a different color disposed around the periphery thereof and each tangent thereto at a single point thereof with no phosphor areas of the same color touching each other. By this arrangement adjacent phosphor areas of one color share intervening phosphor areas of the diiferent color for color-mixing purposes, thus making it possible to provide more phosphor areas per unit space than by the aforementioned ring-dot configuration, hence providing a display of enhanced resolution. In addition, as the electron beam is expanded in diameter to cover an area greater than the area of a given phosphor area, it controllably overlaps and impinges at first on much smaller areas of the adjacent tangent phosphor areas than in the ring-dot arrangment which greatly enhances the controllability of the transition from one color to another. In addition, color transition controllability and uniformity and brightness of color are enhanced by the provision of a storage target or mesh utilizing a square array of square holes.

The invention will be described in greater detail by reference to the drawings in which:

FIGURE 1 shows a cross-sectional schematic view of a storage cathode ray tube embodying the invention;

FIGURE 2 shows an enlarged view of a viewing or phosphor screen for use in a storage cathode ray tube according to the invention;

FIGURE 3 shows an enlarged view of a storage target or mesh in combination and alignment with a viewingscreen for use in a storage cathode ray tube according to the invention; and

FIGURE 4 shows a cross-sectional view of enlarged portions of a storage target and viewing screen according to the invention.

Referring now to the drawings, FIGURE 1 shows a direct-viewing color storage tube comprising an evacuated envelope 2 which includes a large bulbous section 4 having an axially aligned neck portion 6 for housing an electron gun 8 for producing a scanning electron beam of elemental cross-sectional area. Means for orthogonally deflecting the electron beam may be either electromagnetic or electrostatic as is well know in the art and, while not shown, may comprise a deflecting coil disposed externally around the neck portion 6 or deflecting pates disposed internally in the neck portion.

The end of the bulbous section 4 is provided with a faceplate 10 on the interior surface of which is disposed a phosphor viewing screen 12 which will be described in greater detail hereinafter. Adjacent to and co-extensive with the viewing screen 12 there is provided a storage screen 14 supported about its periphery by a ring 16, and a collector grid 18 similarly supported about its periphery by a ring 20.

The storage screen 14 comprises a thin sheet of metal such as cupronickel, for example, of the order of 1 to 6 mils thick. As shown in FIGURE 3 the screen is provided with a plurality of square apertures 22 about 5 inils square, for example. The screen is so formed and positioned in its support ring 16 that the apertures are in proper'alignment with the phosphor areas of the viewing screen as will be more fully explained hereinafter. A storage surface is provided by a layer 24 of dielectric material disposed over the metallic grid portions of the screen on the side thereof opposite the viewing screen 12. The dielectric layer 24 may comprise, for example, a layer of magnesium fluoride of the order of 3 microns thick evaporated on the screen 14.

The collector grid 18 may be provided by either a woven or electro-formed mesh having a pitch of about 250 meshes per inch. This grid is adapted to be maintained at a positive potential with respect to the storage screen 14 for the purpose of collecting secondary electrons emitted from the dielectric layer 24 upon impingement thereof by an electron beam. This potential may be of the order of 120 volts positive with respect to ground.

A source of flood electrons comprises a ring flood gun 26 disposed concentrically about the longitudinal axis of the tube envelope 2. Flood electrons are diffused and collimated over the area of the storage screen by means of the annular electrode portion 28 of the flood gun and an annular funnel-shaped electrode 30 disposed about the preiphery of the collector grid 18 and extending toward the flood gun 26 a distance which is a function of the diameter of the tube. The electrode portion 28 of the flood gun and the funnel-shaped electrode 30 are maintained at a potential that is slightly negative with respect to the potential of the collector grid 18 and may be of the order of 100 volts positive with respect to ground. Additional collimating electrodes, not shown, are provided in the form of annular bands of conductive material applied to the inside surface of the bulbous section 4.

Referring now to FIGURES 2 and 3 an enlarged portion of the viewing screen 12 is shown partially covered by a likewise enlarged portion of the storage screen 14. According to the present invention the viewing screen 12 comprises a plurality of phosphor areas 30 and 32 which are generally rectangular in shape with the corners thereof being somewhat rounded. Phosphor areas 30 are all constituted of a phosphor capable of emitting a single color of light such as green, for example; phosphor areas 32 are likewise constituted of a phosphor capable of emitting a single color of light different to that emitted by phosphor areas 30, such as red, for example. As shown, each phosphor area has four phosphor areas disposed around its periphery and tangent thereto at a single point at the corners thereof with no phosphor areas of the same color touching each other. Thus, each red phosphor area 32 is surrounded in this fashion by four green phosphor areas 30. It will also be noticed that by this arrangement considerable open area or areas not occupied by phosphor material are provided around each phosphor area. The storage screen 14 is mounted in the tube so that the apertures 22 are coaxially aligned with respect to only phosphor areas of a single color which may be the less-efficient light-emitting phosphor; thus, for example, only the red phosphor areas 32 are aligned with the storage screen apertures 22 and are exposed therethrough. It is possible to utilize other arrangements of the storage screen and the viewing screen without departing from the spirit of the invention providedeach phosphor area of one color has a plurality of phosphor areas of a different color disposed around the periphery thereof such that an expanding beam of electrons advances onto the second phosphor in certain directions from the first phosphor before it does in other directions and provided the storage screen is disposed so as to expose only phosphor areas of the same color to a beam of electrons of small cross section coming through the apertures thereof.

' will be excited to emit red light, for example.

The color storage tube of the present invention may be operated in the fashion described in the aforementioned patent to C. D. Beintema. 'In general, a uniform collimated flow of low velocity flood electrons is applied over the entire storage area of the storage screen. The storage surface is prepared for writing by applying a 5 to 10 volt positive pulse to the screen portion which will raise the potential of the storage surface by an amount corresponding to the amplitude of the pulse. The flood electrons then charge the storage surface towards ground potential which may also be the potential of the flood gun cathode. The potentials of the storage surface follow the negative excursion of the trailing edge of the pulse whereby the storage surface eventually assumes a quiescent potential of from 5 to 10 volts negative with respect to ground.

Writing or storage is accomplished by scanning the storage surface with a high energy, high current density electron beam produced by the electron gun 8 and current-modulated in accordance with suitable information signals. This scanning charges the storage surface towards the mean potential of the flood gun cathode or ground by an amount which is a function of the input modulating signal. The potential of the area of storage surface surrounding a given aperture controls the flow of flood electrons through that aperture and thus controls the brightness of illumination of the corresponding phosphor area in a manner hereinafter explained.

Referring to FIGURE 4, if the storage surface about a specific aperture 36 of the storage screen 14 is charged in the range of from 5 to '3.5 volts with respect to the flood gun cathode, the flood electrons designated generally by reference numeral 42 are just able to pass through the aperture 36 and only the phosphor area 32 The etfect of the charge surrounding the aperture 36 is an electron lens effect which focuses the flood electrons on the phosphor area 32 which is in alignment with this aperture. If the storage surface surrounding an aperture such as the aperture 33, for example, is charged in the range of from 3.5 to 1.5 volts relative to the flood gun cathode, the lens effect produced around the aperture permits the flood electrons to penetrate through the aperture in such a manner as to impinge not only on the phosphor area 32 which is aligned with the aperture but also on the corner portions of the phosphor areas 30 which are disposed around the periphery of the phosphor area 32 as described previously. Thus, phosphor area 32 is energized to produce red light and controllably selected portions of the adjacent phosphor areas 30 are also energized to produce green light. The resulting combination of red and green light produces light which appears yellow to the eye. The flood electrons passing through the apertures may thus be controlled and focused so as to form a spot whose diameter may be restricted or expanded to impinge only on phosphor areas of a single color or on different phosphor areas capable of producing a diflerent color. It is in this mechanism that the phosphor target arrangement of the present invention offers a marked advance over the prior art wherein the phosphor areas comprised a dot of phosphor of one color surrounded by a ring of phosphor of a different color. Expanding the flood beam in the ring-dot arrangement tended to introduce too much of the ring phosphor material to the action of the impinging flood electrons and the transition from one color light to another was therefore extremely difficult to control.

So far, storage surface charge conditions have been described which will produce light from a first color phosphor area or a mixture of light from phosphor areas of a second color. By expanding the flood beam spot even more, the second color light can be produced so as to override the first color light whereby only the second color light is observed. In order to do this the phosphor areas producing the second color light should be more eflicient than the phosphor areas producing the first color light. This condition is realized by utilizing phosphor materials capable of producing green and red colors, for example, the green phosphor being more eflicient than the red. Hence, as described previously, the red phosphor areas such as the areas 32 are disposed in alignment with the apertures in the storage screen and the more eflicient green phosphor areas 30 are disposed about the periphery thereof and portions thereof are gradually introduced to the action of the flood electrons. To achieve predominance of the green light, the storage surface surrounding a specific aperture such as 40 is charged to a potential which is from 1.5 to volts with respect to the flood gun cathode. The resulting lens action at the aperture permits a flood beam spot of maximum diameter to fall on the red phosphor area 32 as well as on substantial portions of the adjacent green phosphor areas 30 as shown in FIGURE 4.

It is thus apparent that as the storage surface surrounding the apertures in the storage screen is charged in a positive direction from to 0 volts relative to the flood gun cathode potential, the colors produced by the flood electrons on the viewing screen range in a spectrum from red to green including mixtures thereof.

There thus has been described a cathode ray color storage tube having more uniformity of color and brightness and better controllability of the transition from one color to another. Also by the present arrangement of the phosphor areas on the viewing screen more phosphor areas can be provided thereon than by the ring-dot configuration of the prior art which results in a display of enhanced resolution.

What is claimed is:

1. A direct-view storage tube comprising a storage target having an array of square apertures, means for producing a charge pattern on said storage target, means for directing flood electrons uniformly over said storage target, and a viewing screen adjacent said storage target having a plurality of substantially square spaced areas capable of emitting light of a first color and a plurality of substantially square spaced areas capable of emitting light of a second color disposed around the periphery of each of said first-named areas and tangent thereto at only one point, said first-named areas being aligned with said square apertures in said storage target.

2. The invention according to claim 1 wherein said first-named areas emit light of red color and said secondnamed areas emit light of green color.

3. A direct-view storage tube comprising a storage tar get having an array of square apertures, means for producing a charge pattern on said storage target, means for directing flood electrons uniformly over said storage target, and a viewing screen adjacent said storage target having a plurality of substantially square spaced areas capable of emitting light of a first color and a plurality of substantially square spaced areas capable of emitting light of a second color disposed around the periphery of each of said first named areas, said first and second named areas being tangent to each other at only the corner portions thereof, said first named areas being aligned with said square apertures in said storage target.

References Cited by the Examiner UNITED STATES PATENTS 2,619,608 1l/1952 Rajchrnan. 2,802,964 8/ 1957 Jesty. 2,910,617 10/1959 Smith. 2,962,623 11/ 1960 Beintema.

GEORGE N. WESTBY, Primary Examiner.

ARTHUR GAUSS, C. O. GARDNER,

Assistant Examiners. 

3. A DIRECT-VIEW STORAGE TUBE COMPRISING A STORAGE TARGET HAVING AN ARRAY OF SQUARE APERTURES, MEANS FOR PRODUCING A CHARGE PATTERN ON SAID STORAGE TARGET, MEANS FOR DIRECTING FLOOD ELECTRONS UNIFORMLY OVER SAID STORAGE TARGET, AND A VIEWING SCREEN ADJACENT SAID STORAGE TARGET HAVING A PLURALITY OF SUBSTANTIALLY SQUARE SPACED AREAS CAPABLE OF EMITTING LIGHT OF A FIRST COLOR AND A PLURALITY OF SUBSTANTIALLY SQUARE SPACED AREAS CAPABLE OF EMITTING LIGHT OF A SECOND COLOR DISPOSED AROUND THE PERIPHERY OF EACH OF SAID FIRST NAMED AREAS, SAID FIRST AND SECOND NAMED AREAS BEING TANGENT TO EACH OTHER AT ONLY THE CORNER PORTIONS THEREOF, SAID FIRST NAMED AREAS BEING ALIGNED WITH SAID SQUARE APERTURES IN SAID STORAGE TARGET. 